https://leetcode.com/problems/rotate-image/
You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise). You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.
Example 1:
Input: matrix = [[1,2,3],[4,5,6],[7,8,9]] Output: [[7,4,1],[8,5,2],[9,6,3]]
Example 2:
Input: matrix = [[5,1,9,11],[2,4,8,10],[13,3,6,7],[15,14,12,16]] Output: [[15,13,2,5],[14,3,4,1],[12,6,8,9],[16,7,10,11]]
Constraints:
n == matrix.length == matrix[i].length
1 <= n <= 20
-1000 <= matrix[i][j] <= 1000
- code
class Solution {
public void rotate(int[][] matrix) {
int n = matrix.length;
for (int i = 0; i < (matrix.length + 1) / 2; i++){
for(int j = 0; j < n / 2; j++){
int temp = matrix[n - 1 - j][i];
matrix[n - 1 - j][i] = matrix[n - 1 - i][n - j - 1];
matrix[n - 1 - i][n - j - 1] = matrix[j][n - 1 -i];
matrix[j][n - 1 - i] = matrix[i][j];
matrix[i][j] = temp;
}
}
}
}
- code
class Solution:
def rotate(self, matrix: List[List[int]]) -> None:
length = len(matrix) - 1
for x in range(len(matrix) // 2):
for y in range(x, length - x):
matrix[x][y], matrix[y][~x], matrix[~x][~y], matrix[~y][x] = matrix[~y][x], matrix[x][y], matrix[y][~x], matrix[~x][~y]
return matrix
- code transpose then 1,4 col exchange, 2,3 col exchange
class Solution:
def rotate(self, matrix: List[List[int]]) -> None:
trans = [[row[i] for row in matrix] for i in range(len(matrix[0]))]
for i in trans:
for j in range(int(len(trans[0])/2)):
i[j], i[len(trans[0])-1-j] = i[len(trans[0])-1-j], i[j]
matrix[:] = trans